A good description of the problem which this application addresses may be found in U.S. Pat. No. 4,842,073 to Himes and Vinson. As described therein, clays and fines normally present in a formation will not obstruct the flow of desired hydrocarbons through the formation unless they are disturbed, typically by contact with aqueous well stimulation fluids. When so contacted, the fines tend to clog the capillary passages of the formation, and the clays, depending on their type and structure, will tend to swell in varying degrees.
Salts such as potassium chloride have been widely used to convert the clays from the sodium form by ion exchange to, for example, the potassium form which is less vulnerable to swelling; the physical introduction of such salts causes difficulties, however, with the preparation of the viscosifying polymeric materials typically used to stimulate the formation. Unsuccessful or difficult attempts to prepare combined KCl-polymer compositions in large quantities at the fracturing site led to the Himes/Vinson invention, as described in the above mentioned '073 patent.
Himes and Vinson propose to use various relatively high molecular weight ammonium, morpholinium and pyridinium halides as cations to exchange with the sodium of the clays. They describe the reduction of clay swelling and the maintenance of formation permeability when such cationic compounds are used in conjunction with the stimulation or treatment fluids, such as aqueous solutions of polymers, gels and the like. However, the ccmpositions described by Himes and Vinson generally have a low charge density and to that extent are inefficient; moreover, many compounds used for clay treatment cause undesirable foam during solution preparation and use.
Our invention is also effective to provide relief from the difficulties described in Himes and Vinson U.S. Pat. No. 4,974,678, such as the adsorption of polysaccharides from fracturing fluids by the clays present in subterranean formations.